United States Published Patent Appin. No. 2002/0011926 discloses a device for detecting objects which enter the area of the blind spot of a vehicle during travel. For this purpose, the device essentially uses a system of transmitters which emit a circularly polarized signal, and receivers which receive the echo of this signal. If a turn signal is activated and another vehicle is detected in the vehicle's blind spot, a warning signal is triggered at the side mirror and/or the interior rear-view mirror. If a vehicle having the device passes another vehicle while using the turn signal, a warning is triggered as soon as the passed vehicle enters the blind spot.
United States Published Patent Appin. No. 2006/0006988 discloses a warning indication system which warns drivers of objects in the blind spot of a vehicle with the aid of a luminous display. The warning indication system is connected to a sensor system which indicates to the warning indication system that there are objects in a monitoring area. The warning indication system detects whether the vehicle is expected to change lanes with the aid of a lane change detection routine. The sensor system and the lane change detection routine pass their results to the warning indication system as input values. The warning indication system calculates parameters from these input values, for example, luminosity values, with which the luminous display is controlled, thus generating an adjusted warning signal to be provided to the driver.
Warning systems according to the related art have the disadvantage of triggering warnings in various traffic situations which may be perceived by the driver of a motor vehicle as being incorrect or annoying. For example, if a driver passes another motor vehicle and receives a warning when the passed motor vehicle enters the blind spot, this warning is perceived to be superfluous. Furthermore, a warning signal generated during a passing maneuver distracts the driver and is thus detrimental to traffic safety. On the other hand, if warning signals are triggered with a delay, the driver has a reduced reaction time in critical traffic situations, for example, when changing lanes. Drivers tend to interpret a delayed warning as a malfunction in the warning device and become accustomed to ignoring the apparently unreliable warning device. The effectiveness of warning systems in enhancing traffic safety is therefore diminished.